Earth Resistivity Test on concrete base 3

[Forum Researcher]

Hi, I am planning to conduct an Earth Resistivity Test on my property. The issue is that my building's basement is entirely covered with concrete and pavement, and we intended to use the Fall-of-Potential test method since there are no other equipment options available for rent in my location. However, I am unable to place the probes wherever I need to take the readings. Therefore, I have a few questions:
1. Is it possible to use the other earthing rod/pit as one of the probes?
2. Does the length of the probe matter? If yes, what changes may require in calculation of resistivity?
3. Is there an alternative method to perform the test without expensive equipment?
4. What are the best practices for situations like these?

 

[jghrist]

What is the purpose of the test? Fall-of-potential is a 3 point method to measure ground electrode resistance. Ground resistivity is tested to provide the soil characteristic needed to design a grounding electrode system or to calculate the resistance of a grounding electrode. Ground resistivity uses 4 points. Id the grounding electrode system inside the building basement?

What do you mean by "the other earthing rod/pit"? Do you have two interconnected electrodes?

The length of the probe matters, but not much if the probe spacing is large in comparison to the probe length.
 
There isn't an alternate method without fairly expensive equipment.

You can get lots of information on websites of tester manufacturers like fluke.com, aemc.com, or megger.com

 

[waross]

Does your basement concrete have a vapour barrier?
If the concrete is in contact with the soil, then a connection to a re-bar will probably be the best possible ground.
The concrete dopes the soil and greatly lowers ground resistance.
Google "Ufer ground".

History

During World War II, the U.S. Army required a grounding system for bomb storage vaults near Tucson and Flagstaff, Arizona. Conventional grounding systems did not work well in this location since the desert terrain had no water table and very little rainfall. The extremely dry soil conditions would have required hundreds of feet of rods to be driven into the earth to create a low impedance ground to protect the buildings from lightning strikes.

In 1942, Herbert G. Ufer was a consultant working for the U.S. Army. Ufer was given the task of finding a lower cost and more practical alternative to traditional copper rod grounds for these dry locations. Ufer discovered that concrete had better conductivity than most types of soil. Ufer then developed a grounding scheme based on encasing the grounding conductors in concrete. This method proved to be very effective, and was implemented throughout the Arizona test site.

After the war, Ufer continued to test his grounding method, and his results were published in a paper presented at the IEEE Western Appliance Technical Conference in 1963.[1][2] The use of concrete enclosed grounding conductors was added to the U.S. National Electrical Code (NEC) in 1968. It was not required to be used if a water pipe or other grounding electrode was present. In 1978, the NEC allowed 1/2 inch rebar to be used as a grounding electrode [NEC 250.52(A)(3)]. The NEC refers to this type of ground as a "Concrete Encased Electrode" (CEE) instead of using the name Ufer ground.

Over the years, the term "Ufer ground" has become synonymous with the use of any type of concrete enclosed grounding conductor, whether it conforms to Ufer's original grounding scheme or not.[3]

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Forum Researcher (Electrical)(OP)31 Oct 23 13:53
[COLOR=[i]#3465A4]".#1.. I am planning to conduct an Earth Resistivity Test on my property. The issue is that my building's basement is entirely covered with concrete and pavement, and we intended to use the Fall-of-Potential test method since there are no other equipment options available for rent in my location."[/color][/i]
What is the reason that you are going to conduct earth resistivity test? If you wish to do it , you may carry it out at any short distance say <5m away from your building, The soil composition which make up the earth conductivity in close proximity is NOT expected to vary significantly.
Note: the terminology of "earth resistivity" is different from "earth resistance"
[COLOR=[i]#3465A4]" #2... I am unable to place the probes wherever I need to take the readings. Therefore, I have a few questions:
1. Is it possible to use the other earthing rod/pit as one of the probes?"[/color][/i]
No. Conduct per the connection shown in the test set by the OEM.
[COLOR=[i]#3465A4]" 2. Does the length of the probe matter? If yes, what changes may require in calculation of resistivity?"[/color][/i]
No. insert the OEM probe 400mm approx into the earth would be fine.
" 3. Is there an alternative method to perform the test without expensive equipment?"
Refer test set OEM manual. The test is simple.
[COLOR=
[i]" 4. What are the best practices for situations like these?"[/i]
Conduct the earth resistivity or earth resistance at say within 3m from the building would give you good indication.
Che Kuan Yau (Singapore)

 

[Forum Researcher]

What is the purpose of the test? Fall-of-potential is a 3 point method to measure ground electrode resistance. Ground resistivity is tested to provide the soil characteristic needed to design a grounding electrode system or to calculate the resistance of a grounding electrode. Ground resistivity uses 4 points. Id the grounding electrode system inside the building basement?

What do you mean by "the other earthing rod/pit"? Do you have two interconnected electrodes?

The length of the probe matters, but not much if the probe spacing is large in comparison to the probe length.

There isn't an alternate method without fairly expensive equipment.

You can get lots of information on websites of tester manufacturers like fluke.com, aemc.com, or megger.com

I am required to submit the earth resistivity test reports as part of the local authority's annual audit; if I don't, I will be fined.
About 40 earth pits on my property need to be tested; some of them are clustered together quite closely. Therefore, I was considering using a few of the earth points as probes.
Setting audit aside, I need to inspect the ground points in order to verify the safety of the expensive equipment as well.

 

[jghrist]

It sounds like the requirement would be for an earth resistance test, not an earth resistivity test. You wouldn't do an earth resistance test on existing earth pits. Are the earth pits connected together? If so, the earth resistance test would be for the whole interconnected earthing electrode system. The fall-of-potential test would require extending the probes beyond the zone of influence of the electrode system, which could be very large. If the system is connected to a utility grounded neutral at the service entrance, then measuring resistance with a ground clamp tester may be more appropriate.

If the requirement really is an earth resistivity test, then conducting a test a distance away from the building as suggested by che12345 would be appropriate.